Jill, did you contact them about your missing OBC and other items when you got back? I work for an agency that also frequently offers such promotions. Being human, I have made errors in the past and missed clicking the tab on the booking process we use to get such items purchased by our Accounting Dept. When such an error is made the company, when notified of the mistake sends a check to clients in the amount of such errors.
There have also been times when a promo was not combinable with certain perks. Such a situation should have been disclosed up front before the booking was complete though. If this was recent, call the agency and let them know an error was made. One way to always be sure you'll get anything offered is to be sure such things show on your confirmation when you recieve it. I don't know anything about the agency you used but it may have been an innocent mistake.